I could probably figure out how many miles I had on the original when I bought the second. I don't know off hand how many it was, it's probably in this thread somewhere. I don't use the two evenly. I can only have one plugged in to the bike at a time and I will more or less keep using and recharging the one that's plugged in and switch only when it's dead. I may be on the other for a while or not long at all depending on how I use it.